The present invention relates to optical storage techniques, and more particularly, to methods and apparatuses for extracting specific bits or bytes from BIS data.
According to the specification of the blu-ray disc, a cluster read from an optical disc comprises a BIS (burst indicator subcode) cluster and an LDC (long distance code) cluster. The cluster comprises sixteen address units. The address information of these address units is recorded in the BIS cluster. In decoding, the BIS cluster of 3 columns by 496 rows must be converted into a BIS block of 24 columns by 62 rows. This conversion is necessary in the effort to correct errors of the BIS data.
FIG. 1 shows a schematic diagram of a typical BIS block 100. The BIS block 100 contains 30 rows of data (including 6 rows of physical address information and 24 rows of user control data) and 32 rows of parity information. Each column of the BIS block 100 is a BIS codeword, which contains 6 bytes of physical address information, 24 bytes of user control data, and 32 bytes of parity information. In other words, the BIS block 100 has 24 BIS codewords denoted as BIS codeword 0 through BIS codeword 23 starting from the left and working to the right. During the decoding operations, errors of a BIS codeword may be corrected based on the parity bytes of the BIS codeword.
The 6 rows of physical address information of the BIS block 100 are utilized for recording the sixteen address fields (AFs) of sixteen physical sectors of a physical cluster. Each address field consists of nine bytes of data, wherein the first four bytes are an address unit number (AUN) of a corresponding physical sector, the fifth byte is a flag byte that is utilized for recording flag bits, and the last four bytes are parities of the address field. In FIG. 1, each byte of the sixteen address fields is denoted as AF_n,m where m is the number of the address field and n is the byte number of the address field. For example, AF_4,1 indicates the byte four of the address field one.
As is well known in the art, the nine bytes of an address field are not recorded in contiguous positions of the BIS block 100. Instead, the nine bytes are interleaved into different BIS codewords. For example, the nine bytes of the first address field (i.e., the address field zero), AF_0,0, AF_1,0 through AF_8,0, are respectively byte 0 of the BIS codeword 0, byte 0 of the BIS codeword 1, byte 0 of the BIS codeword 2, byte 2 of the BIS codeword 5, byte 2 of the BIS codeword 3, byte 2 of the BIS codeword 4, byte 4 of the BIS codeword 7, byte 4 of the BIS codeword 8, and byte 4 of the BIS codeword 6. As shown in FIG. 1, since the first four bytes for recording the AUN of the address field zero are not located in contiguous positions, the efficiency of reading the AUN of the address field zero by the conventional optical storage device is reduced accordingly. In fact, the same problem is encountered during the process of reading other address unit numbers.
As mentioned previously, there are sixteen address fields in the BIS block 100 and the flag byte (i.e., the fifth byte) of each address field recorded with important flag bits. FIG. 2 is a flag bit list 200 of a typical BIS data. As shown in the flag bit list 200, for each of the sixteen flag bytes, the bit 7 and bit 5 are status bits of an even data frame of the physical cluster; bit 6 and bit 4 are status bits of an odd data frame; bit 2 is recording date bit; and bit 1 and bit 0 are address bits for recording the address of the last recorded data. In addition, bit 3 of the eight address fields AF_4,0, AF_4,1, through AF_4,7 is a recorder ID tag number IdT_I.
Similar to the aforementioned address fields, the sixteen flag bytes are interleaved into different BIS codewords instead of being stored in contiguous positions of the BIS block 100. Therefore, the efficiency of reading the flag bits recorded in the flag bytes by the conventional optical storage device is undesirable as its performance is limited by the BIS data arrangement. The reading efficiency of the address fields or flag bits significantly affects the accessing speed of the blu-ray disc. There is, therefore, a need for methods and apparatus to improve the accessing efficiency of the address fields or the flag bits mentioned previously, or both.